This invention relates to wireless communications, in general, and to frequency generation circuitry and methods of operating a transceiver having frequency generation circuitry, in particular.
Cellular telephones operate under a wide variety of wireless protocols. Examples of such wireless protocols include a digital cellular service (DCS) wireless protocol, a Global System for Mobile Phones (GSM) wireless protocol, and an enhanced GSM (EGSM) wireless protocol. Other examples of such wireless protocols include a time division multiple access (IS-136 TDMA) wireless protocol and its precursor North American digital cellular (NADC) wireless protocol. Still further examples of such wireless protocols include an integrated digitally enhanced network (IDEN) wireless protocol, and an advanced mobile phone service (AMPS) wireless protocol.
In the past, cellular telephones operated under a single wireless protocol, but new cellular telephones are capable of operating under two or more wireless protocols. An example is a cellular telephone that operates primarily on a GSM system using the GSM wireless protocol, but can roam outside the GSM system and register on a TDMA system using the IS-136 TDMA wireless protocol. However, these new cellular telephones use extremely inefficient and costly circuitry to down-convert a received radio frequency (RF) signal on multiple frequency bands, to up-convert a signal for wireless transmission on multiple frequency bands, to generate internal clock signals for the microcontroller, and to generate timing signals for the data interfaces to the digital signal processing circuitry.
The circuitry used in single protocol cellular telephones is often reused in multiple protocol cellular telephones in a parallel manner. However, this mere aggregation of old circuitry produces a high parts count and complex programming in the new cellular telephones. An example is a cellular telephone operating under the GSM wireless protocol that has an AMPS accessory module that interfaces to the back housing of the cellular telephone to permit the cellular telephone to also operated under the AMPS wireless protocol. This implementation of a dual protocol GSM/AMPS phone is inefficient in terms of redundant and costly circuitry.
Accordingly, a need exists for a frequency generation circuit and method of operating a transceiver comprising the frequency generation circuit that efficiently and cost-effectively down-converts a received RF signal on multiple frequency bands, up-converts a signal for wireless transmission on multiple frequency bands, generates internal clock signals for the microcontroller, and generates timing signals for the data interfaces to the digital signal processing circuitry. Furthermore, a need exists for the frequency generation circuit and method of operating a transceiver comprising the frequency generation circuit to be capable of operating under at least a majority of the wireless protocols.